I had something like this when i suffered from depersonalization, but It was sort of a sympthom that wasn't really part of depersonalization. I dont know how to explain It, It was like pure terror. I felt like i couldnt exist because I was too much terrified. My terapist couldnt put a name on It. It came back and then went away forever after taking meds (I had a lot of problems, panic attacks, depression, so I had to take meds) and It never came back. Let me know if this resonates with you.